The present invention relates in general to mounting arrangements for quartz crystal-packages and more particularly to a low-profile crystal package which may be utilized in high-G environments without damage to the crystal plate inside.
In recent years, space limitations within communications equipment have required smaller and stronger crystal mounting assemblies. This has caused an increase in the electrical and mechanical problems of adequately fixturing and mounting a crystal plate within a crystal package, while not damaging the crystal plate, maintaining frequency standardization of the crystal plate and avoiding internal environmental contamination during the hermetic sealing process. Likewise, as crystal applications have become more and more complex, multiple electrical contact points are required, on smaller and thinner crystal plates being mandated by the higher operating frequencies of the associated electronic equipment. All of these developments have increased the mechanical complexity of the crystal package utilized to protect, house and ease the multiple electrical connections required by multipole crystal filter components.
As the demand for portability of personal communications and electronic equipment continues to increase, the internal electrical components have to be packaged in a manner sufficient to withstand sudden occurrences of high-G forces, in the 2,000-8,000-G range, which occasionally result from the electronic equipment's being accidentally dropped by the user. Various shock-resistant crystal-mounting approaches have been attempted in the past with varying degrees of success.
New bonding methods have been developed as the size of the crystal plate has deceased. The foremost methods in the art are the various ultrasonic scrubbing-wire- bonding approaches used. This process requires that the crystal plate be supported at the contact point during the bonding process when the required pressure is applied to the surface of the plate, as dictated by the bonding process. The crystal plate has to be supported, yet remain undamped and usable thereafter. Therefore most crystal packages have to be made to facilitate automatic wire-bonding between the crystal plate and the crystal package.
Today there are various types of crystal-mounting apparatus which are in common usage. In one approach, the quartz crystal wafer is supported by a center mounting post, which allows the horizontal mounting of the crystal and reduces the overall height of the crystal-package assembly. A disadvantage of this crystal-mounting approach is that the crystal plate needs to be supported adequately during the wire-bonding process so as to withstand the surface pressures involved without sustaining damage. During assembly of the crystal plate onto the respective center-post-mounting position, it is desirable to avoid overstressing the plate, which can result from the means of mounting the crystal plate in the crystal package or from the mechanical stresses which develop during the hermetic sealing of the crystal package. Another disadvantage of this mounting approach is that the crystal plate cannot undergo metallization of the electrode pattern on either side once the plate has been mounted within the crystal package, since the center mounting post requires a plate which has the electrode pattern deposited prior to fixturing and mounting within the crystal package.
The prior-art sealing techniques have generally consisted of the steps of sealing a pair of terminals in an eyelet to form a header, mounting a crystal wafer on an associated header, and hermetically sealing the header to a protective metal or glass container, with the crystal wafer positioned within the container. Headers have been characterized either as matched-glass or compression-glass headers. In both the integrity of the terminal to eyelet seal is dependent upon the attainment of a good seal between the terminal and the glass. Once sealed, the crystal package can be used in many different low-G environments with a high degree of confidence that the internal crystal plate will perform at the desired frequency. A common disadvantage is that a sudden shock or experience of high-G forces will result in the breakage of the internal crystal plate with a corresponding loss of performance.
Another disadvantage of crystal packages is that typically such are assembled from metallic subcomponents, which means that the overall crystal-mounting structure is not compatible with present hybrid microelectronic technologies. Suitable high-G packages of various crystal oscillators for environments involving hybrid mountings do not yet exist.
A disadvantage common to all of the prior-art devices involves the relatively high cost and complexity of most crystal package apparatus.